Android continues to inch its way higher as the leading mobile OS on Millennial Media, according to the ad network's October Mobile Mix report.

Google's mobile platform grabbed 56 percent of all ad impressions on the network last month, double iOS's 28 percent share, figures that include both smartphones and tablets together. Android has been the leading mobile OS on Millennial Media's network for almost a year now.

Among the rest of the pack, RIM's BlackBerry OS took home a 13 percent share, leaving 1 percent each for Nokia's Symbian, Microsoft's Windows Phone, and a range of other mobile platforms.

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Though it lost the smartphone OS crown to Android, Apple is still tops among mobile device makers. Apple devices altogether won 23.5 percent of all ad impressions last month, giving the company the lead among the top 15 manufacturers. The iPhone itself was the most popular device on the top 20 list of mobile phones with a 12.5 percent share.

HTC captured second place with 18 percent of all impressions. Four HTC phones were on the top 20 list, including the Desire, Evo, Droid Incredible, and MyTouch 4G Glacier.

Following closely in third place was Samsung with a 17 percent share. The Korean phone maker grew 7 percent from the previous month and saw six of its phones on the top 20, including the Nexus S and the Galaxy S, both of which hit the list for the first time.

Chinese handset maker Huawei also continued to prove popular, holding onto the #7 position on the list of the top 15 manufacturers. Two of its phones, the Ascend and the Ideo, found spots on the top 20 list of mobile phones. On the list for three months in a row, the Ideo has moved up three spots since August.

Overall, Android devices accounted for 14 of the top 20 mobile phones last month, giving them a combined share of 24 percent of all ad impressions.